Modern Times

It is clear that eclipses have had an importance in the development of human society far beyond people simply wondering at their origin. Eclipses provided the measuring stick with which the year was determined, resulting in accurate calendars. From time to time they startled the ancients, perhaps precipitating pivotal moments in history, as the darkening of Sun or Moon was seized upon as a

FIGURE 3-6. In King Solomon's Mines the author H. Rider Haggard described his British heroes escaping from their African captors by using an eclipse listed in their almanac. Here the natives stare terrified at the darkened Moon, while the former captives make good their escape.

propitious omen by some wily commander or feared by a superstitious enemy. The ability to foresee when eclipses would be witnessed allowed more scientific cultures to impose their will upon others, as in the case of the subterfuge conducted by Christopher Columbus.

Seeing the curved profile of the Earth cast onto the Moon, the ancient Greeks reasoned that the planet is spherical, and this was backed up by other simple observations like the finite curved horizon espied from the top of a mountain. The eventual acceptance of that notion, and the Earth's movement about the Sun in common with the other planets and celestial wanderers like comets, led at last to an understanding of the lunar motion. From that comes our ability to predict eclipses independent of any past record: I can run a computer program using the lunar and solar orbits, printing out when the bodies align with utmost precision, without direct reference to any past eclipse.

Such a computer program may be complicated, but basically it uses the simple gravitational theory of Isaac Newton. We have studied the eclipses of the past, through to Newton's time, but now we might like to come a little more up to date. That involves an interstitial step, though, in which eclipse observations were employed to show that although Newton's theory is a good approximation, it is not a one hundred percent accurate description of the universe.

About the time Charlie Chaplin was making his earliest movies, eventually culminating in Modern Times, eclipse observations were likewise starting to enter their own modern times and being used to verify Albert Einstein's Theory of Relativity. That is the subject to which we now turn.

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